Computer systems include numerous electrical components that draw electrical current to perform their intended functions. For example, a computer's microprocessor or central processing unit (“CPU”) requires electrical current to perform many functions such as controlling the overall operations of the computer system and performing various numerical calculations. Generally, any electrical device through which electrical current flows produces heat. The amount of heat any one device generates generally is a function of the amount of current flowing through the device.
Typically, an electrical device is designed to operate correctly within a predetermined temperature range. If the temperature exceeds the predetermined range (i.e., the device becomes too hot or too cold), the device may not function correctly, thereby potentially degrading the overall performance of the computer system. Thus, many computer systems include cooling systems to regulate the temperature of their electrical components. One type of cooling system is a forced air system that relies on one or more cooling fans to blow air over the electronic components in order to cool the components.
The cubic feet per minute (“CFM”) of air that can be moved across an electric device is an important factor in how much heat can be removed from the device. Thus, the capacity of a cooling fan is a critical factor in selecting an air mover for use in a cooling application. The CFM that a cooling fan can produce is governed a number of factors including: the total area of the blades generating the airflow, the free area provided for airflow through the fan, the design of the blades, and the power generated by the electric motor.
The electric motors used to power many cooling fans are outer rotor motors that utilize a windings section with magnets disposed outside the windings. As electrical current flows through the windings, the magnets rotate about the axis of the motor. The amount of current flowing through the windings determines the power that the motor produces. One way to generate more power is to increase the size of the windings section, but this increase in size is not without drawbacks. For example, as the diameter of the windings section increases, either the diameter of the fan increases or the free area through the fan decreases. Similarly, as the length of the windings section increases, the length of the fan increases and the windings section may become difficult to properly support in a horizontal orientation. Another drawback to increasing the size of a motor is that the cost of the component parts increases as their size increases.